USGS Global Visualization Viewer
Click on a world map to zoom in on and browse a continuous mosaic of recent cloud-free satellite images, explore archived satellite images.

National Geographic Map Machine
View the surface of Earth, zoom in on any part of the world, displayed as topographical map, city map, or satellite imagery.

Online Map Creation
Select map boundaries & choose a projection, GMT software running server-side generates a PostScript map output.

Azimuthal Equidistant Projection Map generator
Input coordinates or select a city to be centered on this map projection.

Azimuth and Distance Calculator
Computes forward & back azimuth and ellipsoidal great circle distance between two points of latitude & longitude, computation done server-side by the National Geodetic Survey.

Great Circle Calculator
JavaScript applet, calculates ellipsoidal Great Circle distance and forward & back azimuth from coordinates.

Surface Distance Calculator
The JavaScript applet that was largely used to create the distance & direction finder on the locate page of the earthdirections site. Calculations assume Earth to be spherical with a 6366.707 km radius.

How Far Is It
Computes forward & back azimuth and ellipsoidal distance between two points on Earth, enter coordinates or type in city names. Calculations done server-side using the geod program.

MIRP
Geomagnetic declination calculator, Geological Survey of Canada.

GMT
Generic Mapping Tools, a collection of open source unix software for “manipulating geographic and Cartesian data sets”.

iGMT
Graphical interface for using GMT with X11 windows, available for Mac OS X, Linux, Debian and other unix platforms.

OpenMap
Open source Java software, provides “the means to see and manipulate geospacial information”.

PROJ
“performs respective forward and inverse transformation of cartographic data to or from cartesian data with a wide range of selectable projection functions.” Unix and Win32 platforms. Mirror: proj.maptools.org

GEOD
“performs Great Circle computations for determining latitude, longitude and back azimuth of a terminus point given a initial point latitude, longitude, azimuth and distance (direct) or the forward and back azimuths and distance between an initial and terminus point latitudes and longitudes (inverse).” Unix and Win32 platforms.

Geodesy and Tcl
T. Vincenty’s algorithm “Direct and inverse solutions of geodesics on the ellipsoid with application of nested equations” within Tcl code.

TerraVision
Open Source interactive terrain visualization system “allows users to navigate, in real time, through a 3-D graphical representation of a real landscape created from elevation data and aerial images of that landscape.”

MERLIN
Multi-source EnviRonmental data dispLay for INternet archives—a Display System for Environmental Data, a scientific tool for researchers investigating global change and climate issues.

World Wind
Open source software from NASA “…allows any user to zoom from satellite altitude into any place on Earth…in visually rich 3D”. Combines imagery from Blue Marble, LandSat 7 and the Shuttle Radar Topography Mission into a high resolution map of the entire world. MS windows platform only.

FreeGIS Project
Overview of free Geographic Information Systems, free GIS software, free Geo-Data software, and data prepared for direct use.

Open Source GIS
Index of Open Source / Free GIS related software projects.

RemoteSensing.org
“Hosts and supports various open source software projects related to remote sensing, GIS, mapping and advanced image processing.”

MapTools.org
“Resource for the open source mapping community, and a home to many open source projects.”

The SOFT EARTH
Links to Geoscience software available on the Internet.

Palm OS Freeware
Calculate great circle distance, sun rise/set times and other Earth & Sun info on your Palm pda with this free software.

Geodesy For The Layman
Open Source book on Geodesy, the measurement and representation of the shape and size of the earth and its gravitational field.

Navigation on the Spheroidal Earth
Determine navigational geometry along the surface of an oblate spheroid (the shape Earth closely approximates), includes formulas and diagrams.

Calculating great circle distance
How to calculate the shortest distance between two points on the surface of the Earth, measured along surface. Includes formulas, sources & links. The US Census website used to have a similar page at census.gov/cgi-bin/geo/gisfaq?Q5.1, but it seems to be gone now.

Where in the world am I?
How to determine longitude and latitude, from the University of Cambridge’s Millennium Mathematics Project.

Latitude and Longitude
Essay discussing parallels of latitude, meridians of longitude, right ascension & declination, and the relationship between longitude and global time zones.

IGU
International Geographical Union

IUGG
International Union of Geodesy and Geophysics

ASPRS
American Society for Photogrammetry and Remote Sensing “…to advance knowledge and improve understanding of mapping sciences to promote the responsible applications of photogrammetry, remote sensing, geographic information systems, and supporting technology.” Check out the Grids and Datums columns.

Open Geospatial Consortium
Non-profit, international, voluntary consensus standards organization leading the development of standards for geospatial and location based services.

Geodetic Resources
Links to geodetic resources, National Geodetic Survey

GEOID Home Page
From the National Geodetic Survey (NGS), the geoid is the “equipotential surface of the Earth’s gravity field which best fits, in a least squares sense, global mean sea level.”

IERS
International Earth Rotation and Reference Systems Service

INTERMAGNET
International Real-time Magnetic Observatory Network, the global network of geomagnetic observatories that monitor Earth's magnetic field

Blue Marble
“…the most detailed true-color image of the entire Earth to date…a collection of satellite-based observations…seamless, true-color mosaic of every square kilometer of our planet…freely available to educators, scientists, museums, and the public.”

Earth Observatory
NASA website providing new satellite imagery and scientific information about our home planet, with a focus on Earth’s climate and environmental change.

Earth Observation Portal
“a single access point for information and services from Earth Observation…direct access to earth-observing satellite data as well as map servers and cartographic resources.”

Global Change Master Directory
The GMCD is a directory of Earth science data and services from NASA, the goal of which is to “enable users to locate and obtain access to Earth science data sets and services relevant to the global change and Earth science research.”

Digital Earth
“...a digital representation of the planet that will allow people to explore and interact with vast amounts of natural and cultural information”

This Dynamic Earth
From the USGS, an on-line book about the Story of Plate Tectonics. Check out the historical perspective on continental drift, see how a hotspot forms the Hawaiian Islands.

Dispersal of Gondwanaland
Animation of the ancient meta-continent breaking up into the continents we know today.

Degree Confluence Project
“The goal of the project is to visit each of the latitude and longitude integer degree intersections in the world, and to take pictures at each location…another goal is to document the changes at these locations over time.”

Build a Solar System
JavaScript for calculating the orbit radii and diameters of planets in a scale model solar system.

Sun-Earth Day
NASA’s website to “increase science literacy and focus attention on the active Sun and its effects on Earth.”